The WiMAX is a novel air interface standard proposed aiming at the frequency band of microwave and millimeter wave, it can support time division duplex (TDD) and frequency division duplex (FDD), and support selecting channel bandwidth step by step, wherein the bandwidth frequency can be 20 MHz, 10 MHz, 5 MHz, 2.5 MHz or 1.25 MHz, so that the operator can customize service and price for customers.
In virtue of the channel of 20 MHz and optimal modulation (namely, 256 Quadrature Amplitude Modulation (QAM)), the data transmission rate of the WiMAX can reach as high as 70-100 MB/s. Furthermore, adaptive modulation method is added in WiMAX technology, and this method allows wireless devices to select optimal modulation automatically according to link range, noises and other conditions. Besides, orthogonal frequency division multiplexing (OFDM) is also added in the WiMAX technology, this is a modulation/multiplexing/access technology for transmitting signals through a wideband, and similar to the CDMA, the OFDM can also reduce the influence of the following factors to the greatest extent, such as multiple path signal, diffraction, attenuation, and other phenomena related to microwave signal transmission. Besides, Reed Solomon forward error correction (FEC), convolutional encoding and interleaving access algorithm are also added in the WiMAX technology to determine and correct bit error. For the errors which can not be found out by the FEC, automatic repeat equipment (ARQ) function only needs to transmit the error data package again, that is, the errors could be corrected.
In addition, in order to further improve the reliability of the link, transmission and reception diversity and adaptive antenna are also added in the WiMAX technology. In security aspect, this technology comprises the widely used triple data encryption standard (3DES) which is a 168-bit cryptographic key and has highly safe encryption performance.
For developing a WiMAX terminal with mobile performance, the firmware of the WiMAX terminal is not stored in a flash, but stored in some place of a host, wherein the host generally refers to PC or the other hosts which use the WiMAX terminal. Whenever the device is inserted into the host and the system is started up, the firmware will be automatically downloaded to the random-access memory (RAM) of the device. After the download of the firmware image is completed, the real code of the firmware will be running on the CPU of an embedded chip.
The downloaded firmware can visit the hardware units on all chips, therefore, if any code can be downloaded at will, some malicious codes breaking the WiMAX protocol may be run, related agreements may be breached, some un-authorized network may be visited, even the performances of base station (BS) or mobile station (MS) nearby may deteriorate. Furthermore, the firmware may visit code identification non-volatile memory (NVM) with X.509 certificate and device cryptographic key on the chip.
Therefore, to authorize only reliable codes to run on the chip is very important. However, the technical scheme which can prevent the malicious code from running and ensure the correctness and security of terminal starting has not been proposed vet at present.